Download Biology-Chapter-12

Biology Chapter 12 Notes
Chapter 12 Voc. Word list: pedigree, Simple Dominant Heredity, Incomplete dominance, Codominance,
multiple alleles, sex determination, autosomes, Sex-linked traits, and Polygenic inheritance
Patterns of Heredity and Human Genetics
A pedigree is a family tree that indicates genetic traits of every one.
 Has a set of symbols to represent the sex of the individual-For instance a cube shape indicates a
male and a circle indicates a female
 Different colors indicate a trait someone has –For example: Hemophilia as below
Most genetic diseases are caused by recessive alleles.-Most get from both parents
1. Cystic fibrosis (CF) –often found in white Americans (one in 28 carry the recessive allele and one
in 2500 children get the disorder)
a. Lung disease
2. Tay-Sachs disease-often found in Ashkenazic Jews with ancestors in Eastern Europe
a. They are missing the enzyme that allows a certain lipid to be broken down causing the
storage of that lipid
3. Phenylketonuria (PKU)-common in North Americans with ancestors from Norway, Sweden, or
Ireland
a. Missing enzyme responsible for converting phenylalanine to tyrosine-causing storage of
the enzyme and severe central nervous system damage
b. Since phenylalanine is rich in milk it becomes a problem in infancy
c. Most babies are tested at birth in the USA
1
Simple Dominant Heredity-Can be obtained from one parent
1. Cleft chin
2. A widow’s peak hairline
3. Hanging Earlobe
4. Hitchhiker’s thumb
5. Almond shaped eyes
6. Thick lips
7. The presence of hair on the middle section of your fingers
8. Huntington’s disease-Is a lethal genetic disorder
a. Affects the individual’s brain between 30 -50 years old
Incomplete dominance: Appearance of a third phenotype pattern. For instances one parent is a white
flower and one parent is red- offspring can be white, red, or pink
Codominance: Expresses both alleles-causing the phenotypes of both homozygotes to be produced in
heterozygous individuals. Example: Black rooster and a white hen-all the offspring are checkered, some
feathers are white and some are black
1. Sickle-cell anemia
a. Most common in Black Americans whose families originated in Africa and white
Americans with originated in countries near the Mediterranean Sea
b. Blood disease
c. Roughly 1 out of 12 Black Americans have either the trait or the disease
Traits controlled by more than two alleles have multiple alleles. Ex. Three alleles of one gene govern the
feather color of pigeons
 There can be more than 100 alleles to exist one trait
 Blood Groups are associated with multiple alleles
Sex determination- Some traits are determined based on sex of the organism
 22 pairs of chromosomes are autosomes-they all look alike
 The 23rd pair is the sex chromosome –indicating the sex of the organism
Sex-linked traits-Traits are contained on the sex determined pair of chromosomes
 Thomas Hunt Morgan (1910) discovered that fruit flies had sex-linked traits
 Most are carried on the X Chromosome
1. Red-green blindness-X-linked recessive inheritance
 Can’t see the different between green and red
2. Hemophilia-X-linked recessive inheritance
 Famous example is Queen Victoria’s pedigree–Hemophilia A
 They do not have the ability to clot their blood
 More common in males because they get it from their mother
2

Females can only get it if both X chromosomes are affected
Polygenic inheritance-is the inheritance pattern of a trait that is controlled by two or more genes.
 Example-Skin color
Bell Ringer: Read p. 332 about Queen Victoria and Royal Hemophilia –Connection to Social Studies and
state the following:
 How many children were affected per generation?
 How many died from it per generation?
 Did any females die?
 Make a pedigree of the family
3